Surviving on abrasive, low-calorie river foliage requires an aggressive digestive architecture. Capybaras manage this through a specialized herbivorous digestive system centered around a massive, chambered cecum that acts as a natural bioreactor.
Because capybaras are monogastric hindgut fermenters, they lack the four-chambered stomachs of cows or sheep. Instead, coarse grasses move past the stomach and into the cecum, where an ecosystem of symbiotic bacteria breaks down tough cellulose through microbial fermentation. This process extracts volatile fatty acids, supplying up to 70% of the animal's daily energy needs.
Yet hindgut fermentation has an evolutionary catch: the cecum sits downstream of the stomach and small intestine, where primary nutrient absorption takes place. To recover vital amino acids, microbial proteins, and B vitamins generated by cecal bacteria, capybaras rely on cecotrophy.
Early each morning, while resting near the water, capybaras excrete and directly ingest soft, nutrient-dense cecal pellets distinct from their firm afternoon feces. This behavior is a biological necessity. Research confirms that without cecotrophy, capybaras cannot maintain nitrogen balance on a pure grass diet.
Grinding down fibrous marsh grasses around the clock also exacts a heavy toll on their mouths. Capybaras possess open-rooted hypsodont teeth, including long, chisel-like incisors and massive corrugated molars, that continuously grow throughout their lives. The abrasive silica contained inside wild grasses and sedges grinds these teeth down at precisely the rate they emerge from the gum line. Without constant grinding against tough forage, their teeth overgrow, misalign, and cause fatal jaw abscesses.
